The present invention relates to room temperature vulcanizable organopolysiloxane compositions having improved shelf stability, resulting from the use of an effective amount of a tin condensation catalyst having organo radicals attached to tin by carbon-tin linkages and whose remaining valences are satisfied by a .beta.-diketonate group, for example, di(n-butyl)tinbis(acetylacetonate).
Prior to the present invention as shown by Brown et al, U.S. Pat. No. 3,161,614, attempts were made to make stable room temperature vulcanizable (RTV) compositions employing a polyalkoxy end blocked polysiloxane and a monocarboxylic acid metal salt catalyst, such as dibutyltindilaurate. These compositions did not cure satisfactorily. Improved results were obtained by Beers, U.S. Pat. No. 4,100,129, assigned to the same assignee as the present invention, utilizing as a condensation catalyst, a silanol reactive organometallic ester having organo radicals attached to metal through metal-oxygen-carbon linkages. Experience has shown that in instances where silanol reactive organo tin compounds are used as RTV condensation catalysts which have organo radicals attached to tin by tin-oxygen-carbon linkages the resulting moisture curable compositions are often unstable.
As utilized hereinafter, the term "stable" as applied to the one package polyalkoxy-terminated organopolysiloxane RTV's of the present invention means a moisture curable mixture capable of remaining substantially unchanged while excluded from atmospheric moisture and which cures to a tack-free elastomer after an extended shelf period. In addition, a stable RTV also means that the tack-free time exhibited by freshly mixed RTV ingredients under atmospheric conditions will be substantially the same as that exhibited by the same mixture of ingredients exposed to atmospheric moisture after having been held in a moisture resistant and moisture-free container for an extended shelf period at ambient conditions, or an equivalent period based on accelerated aging at an elevated temperature.
Further advances were achieved with the employment of silane scavengers for eliminating chemically combined hydroxy radicals, water, or methanol, as shown by White et al, U.S. Pat. No. 4,395,526, assigned to the same assignee as the present invention and incorporated herein by reference. However, the preparation of these silane scavengers, such as methyldimethoxy-(N-methylacetamide)silane often require special techniques and undesirable by-products can be generated during cure. Further improvements are shown by Dziark for scavengers for one component alkoxy functional RTV compositions and process, Ser. No. 349,695, filed Feb. 17, 1982, now U.S. Pat. No. 4,417,042, assigned to the same assignee as the present invention and incorporated herein by reference.
Organic scavengers for trace amounts of water, methanol and silanol are shown by White et al, Ser. No. 481,524, for One Package, Stable, Moisture Curable Alkoxy-Terminated Organopolysiloxane Compositions, filed Apr. 1, 1983, now U.S. Pat. No. 4,472,551, assigned to the same assignee as the present invention and incorporated herein by reference. Additional scavenging techniques for chemically combined hydroxy functional radicals are shown by Lockhart in copending applications Ser. No. 481,529, now U.S. Pat. No. 4,499,230, Ser. No. 481,527, now U.S. Pat. No. 4,499,229, Ser. No. 481,528 now U.S. Pat. No. 4,477,625 and Ser. No. 481,530, filed concurrently on Apr. 1, 1983 now U.S. Pat. No. 4,467,063.
Although the above discussed techniques for improving the stability of room temperature vulcanizable organopolysiloxane compositions employing a tin condensation catalyst have been found to provide stable, substantially acid-free, curable organopolysiloxanes, a separate organic, inorganic, or organosilicon scavenger for hydroxy functional radicals is required. It would be desirable to make stable room temperature vulcanizable organopolysiloxane compositions utilizing a silanol terminated, or alkoxy terminated polydiorganosiloxane and a tin condensation catalyst which can be used in further combination with an alkoxy silane cross-linking agent and optionally an amine accelerator without the employment of additional materials such as scavengers for hydroxy functional materials.
The present invention is based on our discovery that stable, substantially acid-free, room temperature vulcanizable organopolysiloxane compositions can be made free of scavenger for methanol or hydroxy containing material utilizing as a condensation catalyst a tin compound having two monovalent organo radicals attached to tin by carbon-tin linkages and whose remaining valences are satisfied by .beta.-diketonate group. The tin condensation catalyst used in the practice of the present invention are included within the formula, ##STR1## where R is selected from C.sub.(1-18) monovalent hydrocarbon radicals and substituted monovalent hydrocarbon radicals, and R.sup.1, R.sup.2 and R.sup.3 are the same or different monovalent radicals selected from the class consisting of hydrogen, R, --Si(R).sub.3, aryl, acyl and nitrile.
Some of the silanol terminated polydiorganosiloxanes which can be used to make the stable, substantially acid-free, moisture curable organopolysiloxane compositions of the present invention have the formula, ##STR2## where R.sup.4 is a C.sub.(1-13) monovalent substituted or unsubstituted hydrocarbon radical, which is preferably methyl, or a mixture of a major amount of methyl and a minor amount of phenyl, cyanoethyl, trifluoropropyl, vinyl, hydrogen and mixtures thereof, and n is an integer having a value of from about 5 to about 5000.
Polyalkoxy terminated organopolysiloxane which can be used to make the RTV compositions of the present invention has the formula, ##STR3## where R.sup.4 and n are as previously defined, R.sup.5 is a monovalent radical selected from C.sub.(1-13) hydrocarbon radicals and substituted C.sub.(1-13) hydrocarbon radicals, R.sup.6 is a C.sub.(1-8) aliphatic organic radical selected from alkyl radicals, alkylether radicals, alkylester radicals, alkylketone radicals and alkylcyano or a C.sub.(7-13) aralkyl radical and a is a whole number equal to 0 or 1.
The RTV compositions of the present invention can contain a cross-linking polyalkoxysilane having the formula, ##STR4## where R.sup.5, R.sup.6 and a are as previously defined.
The RTV compositions of the present invention also can contain a .beta.-diketone capable of chelating with the tin condensation catalyst of formula (1), referred to hereinafter as "the chelating ligand". The chelating ligand has been found to impart improved stability to the RTV when utilized in effective amounts and is included by the formula ##STR5## where R.sup.1, R.sup.2 and R.sup.3 are as previously defined.